THREE-DIMENSIONAL NUMERICAL SIMULATION OF DENSITY-DEPENDENT GROUNDWATER FLOW AND SALT TRANSPORT IN AN IRREGULARLY LAYERED COASTAL AQUIFER SYSTEM DUE TO GROUNDWATER PUMPING

The aquifer system is located on the western coast of South Korea and is composed of Quaternary alluvial layers underlain by Jurassic and Cretaceous igneous bedrocks. The alluvial layers have horizontally irregular thickness owing to the bedrock topography. Groundwater has been pumped indiscreetly from the overlying alluvial layers and even from the underlying bedrocks for various agricultural activities. As a result, extensive groundwater depletion and salinization have occurred under seawater intrusion, and the sustainability of coastal groundwater resource has become a significant issue in the area and further in its surrounding areas. In order to evaluate density-dependent groundwater flow and salt transport in the irregularly layered coastal aquifer system due to groundwater pumping, a series of three-dimensional numerical simulations is performed using a multidimensional hydrodynamic dispersion numerical model. In the numerical simulations, hydrogeological heterogeneity and geometrical irregularity within the whole aquifer system are considered as they are measured in the field. The numerical simulation results show that such hydrogeological heterogeneity and geometrical irregularity have significant effects on the spatial distributions and temporal changes of density-dependent groundwater flow and salt transport. Therefore it may be concluded that hydrogeological heterogeneity and geometrical irregularity cannot always be ignored if they are observed in actual aquifer systems, and thus they must be properly considered when more rigorous and reasonable predictions of long-term density-dependent groundwater flow and salt transport induced by groundwater pumping are to be obtained for the optimal management of coastal groundwater resource.